The present invention relates generally to derivatization and patterning of surfaces, and more particularly to the formation of self-assembled molecular monolayers on metal oxide surfaces using microcontact printing and derivative articles produced thereby.
In the field of microelectronic devices, sensors, optical elements and electronic displays, the development of devices that are conveniently and relatively inexpensively produced with a relatively low failure rate is important.
A well-known method of production of such devices is photolithography. According to this technique, a negative or positive resist (photoresist) is coated onto the exposed surface of a substrate. The resist is then irradiated in a predetermined pattern, and irradiated (positive resist) or nonirradiated (negative resist) portions of the resist are washed from the surface to produce a predetermined pattern of resist on the surface. This is followed by one or more procedures. For example, the resist may serve as a mask in an etching process in which areas of the material not covered by resist are chemically removed, followed by removal of resist to expose a predetermined pattern of the conducting, insulating, or semiconducting material on the substrate.
According to another example, the patterned surface is exposed to a plating medium or to metal deposition (for example, under a vacuum), followed by removal of the resist, resulting in a predetermined plated pattern on the surface of the material. In addition to photolithography, x-ray and electron-beam lithography have found analogous use.
While the above-described irradiative lithographic methods may be advantageous in many circumstances, all require relatively sophisticated and expensive apparatus to reproduce a particular pattern on a plurality of substrates. Additionally, they generally consume more reactants and produce more by-products in collateral fabrication steps than is optimal. Further, they are relatively time-consuming.
A need exists in the art for a convenient, inexpensive, and reproducible method of etching a surface according to a predetermined pattern. The method would ideally result in patterns having features in the micron and submicron domain, and would provide for convenient reproduction of existing patterns.
The study of self-assembled monolayers (SAMs) is an area of significant scientific research. Such monolayers are typically formed of molecules each having a functional group that selectively attaches to a particular surface, the remainder of each molecule interacting with neighboring molecules in the monolayer to form a relatively ordered array. Such SAMs have been formed on a variety of substrates including metals, silicon dioxide, gallium arsenide, and others. SAMs have been applied to surfaces in predetermined patterns in a variety of ways including simple flooding of a surface along with more sophisticated methods such as irradiative patterning and microcontact printing.
An example of a SAM that has been extensively studied and has been the subject of several patents is composed of a molecular species having a long-chain alkyl group and a thiol (xe2x80x94SH) group at one terminus. These SAMs are formed on metallic surfaces like gold, silver, copper, etc. For example, U.S. Pat. No. 5,512,131 to Kumar et al. describes patterned transfer of alkyl thiols to metallic surfaces such as gold. Other molecular species capable of forming SAMs on oxide surfaces usually contain, at one terminus, trichloro or trialkoxy silane groups that form covalent bonds with hydroxylated surfaces of metal oxides. The drawback of using silane-containing compounds is that these materials are very reactive, forming crosslinked structures in solution or on the surface of a stamp used for microcontact printing. Trichlorosilanes must be handled under an inert atmosphere to prevent their decomposition. A general description of patterning is found in U.S. Pat. No. 5,900,160 to Whitesides, et al. relating to methods of etching articles via microcontact printing..
Accordingly, a general purpose of the present invention is to solve problems associated with expense, complicated apparatus, and other complications associated with patterning indium zinc oxide (IZO) and indium tin oxide (ITO) surfaces for optical and electronic devices.
One object is to provide a method of conveniently and reproducibly producing a variety of SAM patterns on IZO and ITO surfaces, the pattern having resolution in the micron domain, and being amenable to etching.
Another general purpose of the invention is to provide electronic and optical elements and devices that are conveniently and inexpensively manufactured, and that are adaptable to a variety of systems.
The method of patterning a metal oxide surface comprising the present invention, involves the steps of:
a) providing a solid substrate which may be a silicon wafer, glass, quartz, or polymeric materials such as polyimide, polyacrylate, and polyester coated with a thin metal oxide, preferably IZO and ITO, wherein the thickness of said metal oxide layer is from about 50 to about 1000 nm;
b) providing a stamp having a substantially continuous surface with at least one indentation, said indentation being formed by indenting means;
c) coating said stamp surface with a molecular species terminating in a functional group which is capable of reacting with said metal oxide surface to form a bond between said functional group and said metal oxide surface;
d) positioning said coated stamp on the surface of said metal oxide such that said functional group contacts and reacts with at least a portion of said metal oxide surface to form a bond therebetween;
e) removing said stamp from the surface of said metal oxide to obtain a self-assembled monolayer comprising the reaction product of said functional group of said molecular species and said metal oxide.
The non-contacted portion of said metal oxide surface which is not reacted with said molecular species, is removed by contact with an etchant.
The molecular species used in according with the present invention is an organic compound consisting of an alkyl group terminating with a phosphonic acid group and has the formula [CH3(CH2)nPO3H2], wherein in the alkyl portion, n=5-21.
Alternatively, the molecular species comprises an organic compound consisting of an alkyl group which is fully or partially fluorinated terminating with a phosphonic acid group and has the formula [CF3(CF2)m(CH2)nxe2x80x94PO3H2], where n=0-20 and n+m=5-20.
The present invention provides a method of forming a patterned film of either IZO or ITO by microcontact printing and etching. The method involves contacting the surface of the IZO or ITO film with a stamp to transfer to it a self-assembled monolayer of a molecular species in a pattern. The self-assembled monolayer is contiguous with an exposed portion of the surface of the IZO or ITO film in a second pattern. The IZO or ITO film is removed from the underlying substrate, according to the second pattern, by contacting the exposed portion of the IZO or ITO film with an etchant that reacts chemically with the IZO or ITO and is inert with respect to the self-assembled monolayer.